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Visual learning is dependent on the focusing and orienting of the attentional system. Studies have shown that attentional enhancement and suppression modify the encoding of otherwise identically presented stimuli. Recently functional magnetic resonance imaging (fMRI) studies have shown that activation for an attended target is stronger when there is simultaneous suppression of the distractor. Inhibition of Return (IOR), an attentional orienting task in which an elongated cue-to-target interval suppresses attention at the cued location and enhances attention at the non-cued location, contains simultaneous attentional enhancement and suppression. Previous electroencephalography (EEG) research links the N1 component to attentional enhancement that occurs early in IOR and the Nd250 component to excitatory processes overriding IOR, suggesting that they are good candidates for an ERP study of the IOR effect’s role in memory. The present study utilized IOR to examine the impact of target enhancement and distractor suppression on encoding. In the task, a cue appeared on the left or right 600 ms before participants responded to target images appearing in the cued or non-cued location. Participants were not informed that the images used would be the subject of a subsequent recognition memory test. N1 was studied for differences between target enhancement and distractor suppression during encoding, though the Nd250, which is seen at the midline, cannot be contralaterally separated into targets and distractors. Subjects’ reaction times were marginally faster and memory was significantly better for non-cued relative to cued targets. There was an increased N1 and Nd250 for non-cued relative to cued targets and an increased N1 for cued relative to non-cued distractors, consistent with N1 amplitudes being associated with enhancement. These results suggest that the subjects memories are affected by selective attention during encoding; attentional enhancement of targets and suppression of distractors improves memory encoding.
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